When government spends money on something, it must extract private resources -- that is, tax dollars or borrowings – to pay the bills. Those resources get diverted from other uses that might be far more efficient and effective. “Not all infrastructure projects are worth the investment,” states an October 11, 2010, report from the U.S. Department of the Treasury.

How can we tell which ones are?

That’s not easy, but for a government that is already running the largest deficits, in relation to GDP, since World War II and that has gotten very little economic bang for the bucks it has already spent, the first rule is modesty; do no harm. The second rule is to look to the private sector to make the decisions.

Canning and Pedroni explain that competitive markets do the best job of deciding how much infrastructure to provide and what kind. In other words, they excel at setting “the optimal level of provision.” But, they write, “in practice, infrastructure has often been supplied by the public sector, and we have the possibility of large externalities, perhaps leading to misallocation of resources.”

So, it stands to reason that if the government wants to encourage infrastructure investment – in order to boost economic growth and thus job creation – then the least risky and most effective choice would be to encourage the private sector to risk its own capital and certainly not to stand in the way of such investment.

That’s why it’s so inexplicable that two of the largest prospective infrastructure investments in America are being blocked, or at least delayed, by government. One would result from the merger of AT&T and T-Mobile, which I discussed earlier on Forbes.com. The merger would accelerate deployment of a nationwide LTE 4G wireless network that would bring high-speed broadband to 97 percent of Americans.

The second investment involves energy. Wood Mackenzie, a consulting firm, recently released a report that showed that if the U.S. government allows further sensible energy development projects to go ahead, the results of building and benefiting from the new infrastructure would be over 1 million new jobs by 2018 and over $800 billion in extra government revenues by 2030.

The infrastructure projects include the Keystone XL pipeline, which would bring resources from oil sands from Canada to the U.S., a return to pre-moratorium drilling levels for the Gulf of Mexico, access to many off-limits drilling areas, including offshore Alaska and the Eastern Gulf of Mexico, the lifting of a moratorium on extracting natural gas from shale deposits in New York state, and an end to “unduly burdensome” and “duplicative” environmental regulations involving shale gas.

Lifting the obstacles to expansion of wireless and energy infrastructure in the United States would not cost a penny of taxpayer money. No private resources would be diverted by government. By definition, these outlays of infrastructure would be, in Treasury’s words, “worth the investment.”

In his speech to a joint session of Congress, President Obama outlined a different set of taxpayer-funded infrastructure spending: